1. Field of the Invention
This invention relates generally to fixed lens cameras, and more particularly to a fixed lens camera including a sensory indicator that signals changes in the relative focal distances between successive sample images taken by the camera.
2. Description of the Background Art
Taking a clear, sharp picture using a fixed lens camera with a close up lens attached requires knowing the exact distance between the camera's aperture and the target to be photographed. In other words, the depth of field does not provide for much tolerance in the focal length, and there is a very small distance before and after the focal plane, within which an image will still be clear. When attempting to take a close-up photograph of an object, the use of a close up lens is common. The use of a close up lens in a fixed lens camera decreases the tolerance in the focal length, making for a very shallow depth of field. Movement of the camera, even very small amounts from the optimal focal distance, will cause the image to fall out of focus.
Most people cannot estimate distances accurately enough to effectively use a fixed lens camera having a shallow depth of field to take clear close-up photographs every time. People can estimate larger distances within reasonable tolerances--such as a person's height being six feet, give or take a few inches. However, because the fixed lens camera including a close up lens requires an accurate measurement between the camera and the target, most people will not be able to take a focused, close-up photograph consistently, using this type of camera.
Previous attempts to overcome the shallow depth of field problem in fixed lens cameras include active range finding schemes via infrared light and sonar. Another active method is to provide the camera with a pair of focusing bar LED devices, each of which emit a light beam, where the light beams cross at the focal plane. The camera operator moves the camera toward or away from the object until he sees only one point of light on the object. Passive measurement schemes include providing a length of string or other measuring object whose length is the focal length, and directing the picture taker to use the string to determine the proper distance from the object at which to place the camera. These range finding schemes of the prior art add elaborate components to the camera and make the picture taking process more complex and difficult.
Auto focus cameras have an optimal focal distance measuring system that includes a lens adjusting mechanism, where the mechanism moves the lens in accordance with the measurement taken, in order to automatically focus the camera. Common auto focus systems are not applicable to fixed lens cameras, because the lens in a fixed lens camera is not movable or adjustable.
What is needed is a system in a fixed lens camera that assists the user in determining the proper focal distance of the camera, permitting the user to position the camera at that distance from the object.